1. Technical Field
The present invention relates in particular to a spindle motor to be used in the hard disk drive means.
2. Description of the Prior Art
The spindle motor of the hard disk drive means employes grease or oil as a lubricant to be applied to the rolling bearing.
The lubricant will be splashed and dispersed during the rotation of the motor in high speed. Thus produced finely dispersed lubricant or oil mist is apt to get into the disk enclosure of the hard disk drive means. Further, fine dusts suspended in atmosphere is tend to get through the bearing assembly into the disk enclosure. These oil mist or dusts will cause the malfunction of the hard disk drive means.
In other words, these oil mist or dust adhered on the magnetic disk or the magnetic head will cause the crushing of the magnetic disk and the magnetic head.
In order to prevent these oil mist or dust from getting into the disk enclosure, a number of countermeasures have been taken by those skilled in the art. Among these countermeasures, a method using a magnetic fluid and that using a labyrinth seal of such structure as shown in FIG. 9 are often employed.
However, when the magnetic fluid is employed to seal, the magnetic fluid filling the gab between the shaft or spindle and a magnetic fluid bearing plate is tend to shift radially outwardly under the effect of centrifugal force. Further, the magnetic fluid sometimes splashes under the effect of locally effected differential of air pressure.
In an example of a labyrinth seal illustrated in FIG. 9, recessed pockets IIIa and IIIb are formed on the opposite surfaces of a hub I (a rotational member) and a base II (a stational member). In the structure of the labyrinth seal of FIG. 9, the cost for machining and molding parts of the motor is relatively high.
Accordingly, the object of the present invention is to provide a spindle motor having a sealing means which can easily be assembled into the motor, a sufficient sealing effect can be obtained thereby, and the cost for machining and molding parts of the sealing means can be reduced.
These and other objects are achieved by a spindle motor including a base to which a spindle is secured to extend therefrom, a rotor hub through the central portion of which a vertical bore is provided, and a bearing assembly interposed between the spindle and the bore of the rotor hub, characterized in that a plurality of toroidal sealing plates spaced axially by a slight gaps s1 and s2 are disposed between the spindle and the vertical bore of the rotor hub at above and/or below the bearing apparatus such that the outer or inner peripheral portion of each plate is secured to the inner peripheral portion of the bore of the rotor hub or the outer peripheral portion of the spindle so as to leave a slight radial gaps between the inner or outer peripheral portion of each plate and the outer peripheral portion of the spindle or the inner peripheral portion of the bore of the rotor hub to make each sealing plate uncontacted with the spindle or the bore, wherein the radial gaps are positioned alternately on the side of the spindle or on the side of the bore of the rotor hub.
Alternatively, a spindle motor including a base to which a spindle is secured to extend therefrom, a rotor hub through the central portion of which a vertical bore is provided, and a bearing assembly interposed between the spindle and the bore of the rotor hub, characterized in that a plurality of toroidal sealing plates spaced axially by a slight gaps s1 and s2 are disposed between the spindle and the vertical bore of the rotor hub at above and/or below the bearing apparatus such that the outer or inner peripheral portion of each plate is secured to the inner peripheral portion of the bore of the rotor hub or the outer peripheral portion of the spindle so as to leave a slight radial gaps between the inner or outer peripheral portion of each plate and the outer peripheral portion of the spindle or the inner peripheral portion of the bore of the rotor hub to make each sealing plate uncontacted with the spindle or the bore, wherein the radial gaps are positioned alternately on the side of the spindle or on the side of the bore of the rotor hub, and that a toroidal magnetic field generator is secured in its outer peripheral portion to the vertical bore of the rotor hub, and a magnetic fluid is sustained within a radial gap left between the inner periphery of the generator and the outer peripheral surface of the spindle under the effect of the magnetic force of the generator.